Low-temperature on-site in situ high-pressure ultrafast pump-probe spectroscopy instrument.

We design and construct an ultrafast optical spectroscopy instrument that integrates both on-site in situ high-pressure technique and low-temperature tuning capability. Conventional related instruments rely on off-site tuning and calibration of the high pressure. Recently, we have developed an on-site in situ technique, which has the advantage of removing repositioning fluctuation. That instrument only works at room temperature, which greatly hampers its application to the investigation of correlated quantum materials. Here, we further integrate low temperature functioning to this instrument, by overcoming enormous technical challenges. We demonstrate on-site in situ high-pressure ultrafast spectroscopy under a tunable temperature, from liquid-helium to above-room temperatures. During the pressure and temperature tuning process, the sample neither moves nor rotates, allowing for reliable systematic pressure- and temperature-dependence data acquisition. Ultrafast dynamics under 10-60 GPa at 130 K, as well as 40-300 K at 15 GPa, is achieved. Increasing and decreasing pressure within 5-40 GPa range at 79 K has also been achieved. The precisions are 0.1 GPa and 0.1 K. Significantly, temperature-induced pressure drifting is overcome by our double-pneumatic membrane technique. Our low temperature on-site in situ system enables precise pressure and temperature control, opening the door for reliable investigation of ultrafast dynamics of excited quantum states, especially phase transitions in correlated materials, driven by both pressure and temperature.